The invention concerns transmission techniques for the purpose of communication and possibly location.
It is known how to relay a two-directional link (FIG. 1) by satellite between different stations (A, B1, B2) on the Earth's surface or ground. The link from the main station A to the secondary stations Bi may be a high-power narrow-band link. In the opposite direction, from the secondary stations Bi to the head station A, it is preferable to use a broad-band link: subject to appropriate encoding, a broad-band link allows simultaneous communication from the secondary stations Bi to the main station A.
On board the satellite a repeater is installed, intended to provide appropriate transmission of the signals in the two bands. Conventionally, this repeater provides amplification separately for each of the bands in question.
Although able to function, this solution is not entirely satisfactory, for various reasons. One of these reasons is that the electrical power supply available on board a satellite is necessarily limited. However, though the narrow-band link may be subjected to high-gain (and therefore non-linear) amplification, on the other hand the same obviously cannot apply to the broad-band link. A compromise therefore has to be found between the amplification gain and the electrical power available.
Secondly, amplifying the signals of the two narrow-band and broad-band links respectively on board the satellite separately entails a duplication of certain functions; this is undesirable since the more complex the structure of the satellite the more tricky it is to set it up and maintain it.